How to remove embedded sand from low pass/anti aliasing filter?

Question

I have a canon 50d with obstructions on the sensor.

Before any cleaning:

I have tried to clean the filter with this kit.

After cleaning with a blower (All shots at F36, ISO 100, 135MM, of a white sheet of paper):

After first 2 swab wet cleaning (one wet followed by one dry):

After aggressive wet cleaning, same as above but with multiple passes across the filter and scrubbing one half the filter to see if I could dislodge anything:

100% crop of the image above:

It appears there is granules of sand stuck to the low pass filter and the plastic framing around the sensor:

Here is a cropped view of the top left corner:

Is there a stronger emulsifier I could use on the filter to try to dislodge the granules or another technique I could use to try and remove them?

I have read online about people removing the low pass filters from their cameras so one option might be to remove the filter altogether. The filter has a dust reduction circuitry so this may be more complicated than just removing it Step 17.

Answer 1

I have observed somewhat similar effect on a scientific CMOS camera. We sent it back to manufacturer, and they suggested that it might have been water condensation.

If that's the case for you, any cleaning that is done externally is not going to help, you need to disassemble the sensor, probably remove glass filter (as you call it, anti-aliasing). But that is not the only filter that sits between environment and semiconductor chip:

Since removing of any of these filters have intrinsic chance of failure q, removing three of them has diminishing chance (1-q)^3 of success. But since camera is throw-away, go ahead and let us know your story!

Answer 2

Looks like a professional repair job is needed, or you can look into conversion for infra-red (which basically removes the IR cut filter, and perhaps the low-pass filter).

Answer 3

If you're willing to risk having to write the camera off anyway, you might try very lightly touching it with a loop of cellophane tape (do not press) and see if that helps.

That said, I'd bet there's a decent chance that the reason you can't clean off the particles is that the sand somehow got in behind one of those filter layers, rather than being on the outside.